CN105308149A - Improved phase change compositions - Google Patents

Abstract

Described herein are sodium acetate trihydrate-containing phase change materials with better uniformity, methods of making the materials, and their utility in phase change systems. More particularly, the present invention relates to the use of a phase change composition comprising sodium acetate trihydrate, at least one base for inhibiting the formation of anhydrous sodium acetate crystals in a phase change material containing sodium acetate trihydrate A soluble polymer, at least one sodium acetate trihydrate nucleation promoter, and if a low phase transition temperature is desired, at least one melting point depressant.

Description

Improved Phase Change Composition

technical field

The present invention relates to more uniform phase change materials containing sodium acetate trihydrate, methods of making said materials, and their utility in phase change systems. More particularly, the present invention relates to the use of a phase change composition comprising sodium acetate trihydrate, at least one base for inhibiting the formation of anhydrous sodium acetate crystals in a phase change material containing sodium acetate trihydrate a soluble polymer, and at least one nucleating promoter of sodium acetate trihydrate.

Background of the invention

There are many heating and cooling systems on the market, most of which rely on fossil fuels. With the ever-increasing demand for more environmentally friendly systems, various alternative systems based on sunlight or water have been proposed such as, for example, photovoltaics, solar thermal generators, hydroelectrics, wave power and biofuels.

The problem with all solar-powered renewable energy conversion devices, some water-driven devices, and wind turbines is that they don't run "on demand" because the sun isn't always shining, the waves aren't always high, and the wind isn't always blowing. This means that sometimes the power generated by these so-called intermittent renewable sources will not be easily integrated into their respective local grids, which is why many storage options have been proposed.

The thermal energy storage system proposed in WO2009/138771, when available, converts excess electrical energy obtained from intermittent renewable energy sources into heat or cold energy, stores the thus converted heat or cold energy in a thermal accumulator, and then uses a phase change material (PCMs), through their inherent solid-liquid phase change properties, affect energy conversion, converting it into useful heat or cold energy on demand.

For practical application in domestic situations, there is a need for phase change materials capable of supplying warm water, or even hot water, only slightly above the comfort level of hot water required by the individual. Furthermore, phase change materials suitable for this practical application should transfer heat inwardly and outwardly at a rate commensurate with domestic use as they phase change, and deliver an acceptable level of thermodynamic stability (efficiency).

Sodium acetate trihydrate (SAT) undergoes a solid-liquid phase transition in the desired temperature range for domestic applications. However, the practical application of SAT as a phase change material (PCM) is limited by the unique inconsistent manner of melting from solid SAT to a mixture of liquid SAT and solid (sodium acetate/SA) at a set temperature of 58 °C. The inability to obtain a completely liquid solution at 58 °C is a problem, which is reflected in the thermodynamic stability of the aqueous solution upon initial heating, and the thermodynamic stability of the re-formed aqueous solution obtained by reheating after cooling, following the normal heating/cooling cycle in a phase change system neutral.

The formation of a solid during melting is problematic for the use of SAT as a PCM because once this solid SA is formed, it will generally remain throughout the life of the PCM in the phase change system.

Previous attempts to overcome this problem by using three-dimensionally cross-linked polymers, such as cellulose-based polymers and superabsorbent polymers, as solid supports have not been successful because despite the apparent reduction in initial solid formation, solid The potential problem of sodium acetate formation is not resolved and solid sodium acetate will still precipitate out of solution over time, irreversibly accumulating at the bottom of the PCM storage vessel. A solution with a limited lifetime is not acceptable for application as a PCM.

It is an object of at least one aspect of the present invention to obviate or alleviate at least one or more of the aforementioned problems associated with the use of sodium acetate trihydrate as a potential PCM in aqueous phase change systems.

It is an object of at least one aspect of the present invention to provide improved phase change materials containing sodium acetate trihydrate, which have desirable uniformity, resistance to SA formation, and are suitable for use in phase change systems.

It is an object of at least one aspect of the present invention to provide improved phase change materials containing sodium acetate trihydrate that can be heated, cooled, and reheated repeatedly while maintaining thermodynamic stability.

The applicant has developed a novel inventive aqueous composition for use as a phase change material, which comprises: sodium acetate trihydrate; at least one agent for inhibiting the formation of anhydrous sodium acetate crystals in the phase change material containing sodium acetate trihydrate an alkali soluble polymer; and at least one nucleating promoter of sodium acetate trihydrate. The applicant has also developed a preparation method of the improved phase change material.

Contents of the invention

The applicant has developed a novel inventive phase-change composition, which contains sodium acetate trihydrate as a phase-change material.

Correspondingly, the present invention provides the composition containing sodium acetate trihydrate as phase change material, and it comprises:

(a) sodium acetate trihydrate or sodium acetate anhydrous;

(b) at least one suitable alkali-soluble polymer;

(c) at least one suitable nucleation promoter; and

(d) water.

As shown in the following examples, the applicant has unexpectedly found that the composition containing sodium acetate trihydrate as a phase change material of the present invention is more homogeneous and thermodynamically stable than previously achieved by using sodium acetate trihydrate as PCM. showed unprecedented improvement. In particular, applicants have discovered that sodium acetate trihydrate-containing compositions of the present invention as phase change materials resist nucleation of crystalline sodium acetate upon heating and cooling.

According to another aspect, the present invention provides the use of a composition according to the invention as a phase change material suitable for use in a phase change system.

The applicant has also developed a novel process for the preparation of the compositions according to the invention. According to another aspect, the present invention provides a preparation method of a composition containing sodium acetate trihydrate as a phase change material, comprising:

(a) mixing an aqueous solution comprising anhydrous sodium acetate, at least one suitable alkali-soluble polymer, and at least one nucleation promoter;

(b) heating the resulting mixture to provide a phase change material comprising sodium acetate trihydrate at 58°C.

When using sodium acetate trihydrate, follow these steps:

(a) heating sodium acetate trihydrate to a temperature above 58°C; and

(b) Sodium acetate trihydrate, at least one suitable alkali soluble polymer and at least one nucleation promoter are mixed.

Brief description of the drawings

Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a phase diagram of sodium acetate and water, which shows that at about 58°C, the solubility limit of sodium acetate in water is about 58.0%, whereas the corresponding sodium acetate trihydrate melted at 58°C consists of 60.28% SA and Composed of 39.72% water, the value indicated by point 2 is significantly above the solubility limit at 58°C.

Figure 2 is the proposed mechanism where the polymer interacts with the surface of highly metastable subcritical sodium acetate molecular clusters, preventing or preventing further growth into crystallites by a blocking mechanism and thus precipitating the species in due course.

Figure 3 demonstrates the crystallization temperatures obtained by adding various levels of acetamide.

detailed description

The novel composition according to the invention is an aqueous composition as a phase change material containing sodium acetate trihydrate NaOAc·3H ₂ O, also known as SAT. Anhydrous sodium acetate, also known as SA, in any form can be used in the preparation of the novel SAT-containing composition as PCM according to the present invention. For the avoidance of doubt, this means that since all solid forms of NaOAc are crystalline, any crystalline form may be used.

The level of anhydrous sodium acetate used in preparing the aqueous compositions according to the present invention is between about 40% and about 60% by weight of the total composition. This corresponds to a relative amount of sodium acetate trihydrate of about 66% to about 100% in the aqueous composition of the present invention. For the avoidance of doubt, the compositions according to the invention are substantially free of, and more preferably free of, solid anhydrous sodium acetate.

For the avoidance of doubt, when in any particular composition according to the invention described herein, the actual or relative amount of water is not specified, it is to be understood that the actual or relative amount of water required, whether by weight or relative volume, will be sufficient to make the composition 100%. Purified water, distilled water or water from normal supply may be used.

As noted above, the application of sodium acetate trihydrate as a potential PCM has so far been hampered due to its inconsistent internal melting, despite having a phase transition in the desired temperature range for domestic heating purposes. During melting, at a set temperature of 58 °C, sodium acetate trihydrate transformed from solid SAT to a mixture of liquid SAT and solid. This is due to the formation of anhydrous sodium acetate NaOAc or SA. For the avoidance of doubt, when the term sodium acetate or SA is used herein, it refers to anhydrous sodium acetate, which is distinct from any aqueous form, or specifically sodium acetate trihydrate SAT. As indicated by point 1 in the phase diagram of sodium acetate and water in Figure 1, the solubility limit of sodium acetate in water is about 58.0% at about 58°C, whereas the corresponding sodium acetate trihydrate melted at 58°C consists of 60.28% SA and 39.72% water composition, the value indicated by point 2 in Figure 1 is significantly higher than the solubility limit at 58°C. When SA is formed during the melting of aqueous SAT, the fully liquid state can be restored by adding more water, changing the composition to that of 58% SA, and dissolving anhydrous SA, thereby providing a fully liquid material at 58°C. The solution thus prepared is thermodynamically stable, ie it is neither in the metastable region nor in the supersaturation region, so no additional solid species (SA) will crystallize.

As stated above, this reconstituted liquid solution comprising water and sodium acetate trihydrate is not suitable for use as a phase change agent because it cannot be cooled and then reheated to provide a thermodynamically stable homogeneous liquid. As set forth in the Examples below, Applicants found that when this solution was cooled and seeded with some sodium acetate trihydrate, a solid sample of sodium acetate trihydrate formed. Applicants have also found that when this cooled solution is heated again to 58°C, a solution with some solid anhydrous sodium acetate SA is formed, ie the solution is not in fact thermodynamically equilibrated.

Mixing and/or agitation will return the composition to its thermodynamic equilibrium, homogeneous solution, but without such a mechanism in the present invention, a homogeneous solution will not be obtained.

As shown in Figure 1, crystalline sodium acetate trihydrate is melted to form a concentrate of anhydrous sodium acetate and aqueous sodium acetate. In short, adding more water is expected to dissolve the extra sodium acetate (anhydrous solid), according to normal chemical practice. More precisely, it is expected that this additional water will dilute the concentrate comprising anhydrous sodium acetate and water, thereby dissolving the solid anhydrous sodium acetate therein. Even more surprisingly, applicants have demonstrated that this does not occur in practice, and that the resistance to dissolution of anhydrous solids is virtually unchanged by the additional amount of water.

Without wishing to be bound by any particular theory, it is postulated herein that during the melting process, the sodium acetate trihydrate molecules segregate inconsistently and switch rapidly between liquid phase sodium acetate and solid phase sodium acetate. The solid anhydrous sodium acetate molecules are believed to exist initially in small clusters. It is believed that such small clusters may contain hundreds of SA molecules and are not believed to be crystalline. It is also proposed herein that as any of these clusters increase in size, they can eventually reach the critical cluster size, or threshold size, required to become crystallites. It is also suggested herein that such aggregated crystallites form dense crystals of sodium acetate which were rated as unwanted solid precipitated material in the previous examples. Applicants observed that during melting the formation of a solid precipitate occurred too quickly for the added water to have any appreciable effect on dissolution.

Applicants have solved the problem of non-uniform liquid formation in liquid phase change materials containing sodium acetate trihydrate by providing PCM containing NaOAc·3H ₂ O, by applying one or more special alkali-soluble polymers, resistant to NaOAc Crystallite formation.

Without being bound by any particular theory, it is believed that the specific polymers employed in the PCM containing sodium acetate trihydrate of the composition according to the invention, through a combination of viscosity effects, crystal habit changing behavior, 3D lattice effects, allow Anti-NaOAc precipitate formation in NaOAc·3H ₂ O solution. As such, one or more alkali soluble polymers suitable for use herein may also be considered to be an inhibitor of SA crystallization, or an inhibitor of aqueous solution formation of crystalline SA.

It is believed that in part by exploiting the properties of these particular polymers to increase the viscosity of the solution, at least some of the anhydrous sodium acetate formed during melting can remain suspended for a long time to dissolve and thereby reduce the likelihood of SA precipitation in solution , subsequently reducing agglomeration when used in phase change system equipment. It is also proposed here that the use of these special polymers will provide solid sodium acetate with significantly increased effective surface area in solution, whereas previously possible (for SA-only aqueous systems) when solids accumulate at the bottom, only The top of the solid layer is in contact with the solution. It is also suggested herein that dispersion of solid sodium acetate in this more viscous solution for even longer periods of time may increase the rate of dissolution and thereby reduce the rate of formation of the anhydrous form of sodium acetate and possibly prevent its formation in general.

Polymers useful in the novel SAT-containing compositions as PCM according to the first or further aspects of the invention as detailed herein are soluble in aqueous alkaline solutions. The polymers defined herein for use herein are soluble in aqueous alkaline solutions having a pH greater than about pH 8. More particularly, polymers suitable for use herein are soluble in an aqueous strong base solution having a pH of about pH 9, such as aqueous sodium acetate solution. As defined herein, the compositions herein comprise one or more polymers, wherein the level of each polymer employed in the aqueous compositions according to the invention may independently be from about 0.1% to about 10%, about 0.2% to about 4%, about 0.5% to about 2%.

In addition, the polymers used herein have one or more carboxylic acid groups and can be used as acids or acid salts. For the avoidance of doubt, the term "polymer" as used herein includes polymers that repeat a single monomeric unit, as well as copolymers that include mixed monomeric units with a different repeating pattern.

A preferred group of polymers for use herein are polymers having repeating units of the general formula I and salts thereof:

-{[X] _n -[Y] _m -} _z -

I

where z is from 10 to 1000;

n=1 to 10 to 1000; and wherein m=0 to 1000;

wherein the ratio of n:m is in the range of about X to Y, and wherein the molecular weight of the polymer is in the range of about P to about Q,

X is independently selected from the group based on the following monomers: ethylene, acrylic acid, methyl methacrylate, acrylamide, ethyl methacrylate, ethacrylic acid, diethyl ether, diallyldimethylammonium chloride, vinylpyrrolidone , N-isopropylacrylamide, styrene, maleic acid and mixtures thereof,

Y is independently selected from the group based on the following monomers: ethylene, acrylic acid, methyl methacrylate, acrylamide, ethyl methacrylate, ethacrylic acid, diethyl ether, diallyldimethylammonium chloride, vinylpyrrolidone , N-isopropylacrylamide, styrene, maleic acid and mixtures thereof,

A preferred group of polymers according to general formula I for use herein are polymers having repeating units of monomers of general formula II and salts thereof:

wherein n, m and z are as defined above,

wherein the ratio of n:m is about 1:2, and wherein the molecular weight is in the range of about 1,000 to 1,000,000.

Preferred polymers of general formula II for use herein are acids or acid salts, more particularly acid or metal acid salts, especially acid or acid salts of sodium, potassium or zinc. Copolymers of methacrylic acid and methyl methacrylate having a molecular weight of from about 500,000 to about 1,000,000—poly(methacrylic acid-methyl methacrylate), and their sodium, potassium, or zinc salts are those having the general formula I , II and III polymers, and are especially suitable for use herein.

Another group of preferred polymers according to general formula I for use herein are polymers having monomeric repeating units of general formula III and metal salts thereof selected from sodium or potassium:

and

wherein z and n are as defined above.

A preferred polymer of formula III for use herein is poly(methacrylic acid), especially the sodium salt, preferably as a 30% or 40% aqueous solution, wherein the average molecular weight of the polymer is about 10,000 or 4-6,000.

Accordingly, the present invention provides a composition as hereinbefore defined wherein one or more alkali soluble polymers are selected from formula II or III and mixtures thereof, the level of each alkali soluble polymer independently being from about 0.1% to About 10%, about 0.2% to about 4%, about 0.5% to about 2%. Additionally, in the composition as previously defined, the polymer is: a copolymer of methacrylic acid and methyl methacrylate having a molecular weight of from about 500,000 to about 1,000,000—poly(methacrylic acid-methyl methacrylate), or its sodium, potassium or zinc salt; poly(methacrylic acid) or its sodium salt having an average molecular weight of about 10,000, wherein the level of either polymer is independently from about 0.1% to about 10%, from about 0.2% to About 4%, about 0.5% to about 2%. According to another aspect, the present invention provides a composition having the levels of one or more of the two polymers as described above.

It has been demonstrated that the improved PCM composition containing SAT as PCM according to the present invention forms a homogeneous liquid without the need to add additional water, in sharp contrast to the precipitation system observed without polymer. However, the SAT-containing PCM system of the present invention with the polymer demonstrated improved homogeneity and thermodynamic stability after cooling and reheating compared to the performance exhibited by sodium acetate trihydrate without the polymer, which is Truly revolutionary.

Without being bound by any particular theory, this paper proposes that, in a variety of different SAT/polymer systems, testing the unprecedented delivery of nucleation inhibition in aqueous sodium acetate trihydrate systems, the remarkable performance observed is due to their shared consistent potential technical effect. While the precise mechanism of crystallization nucleation inhibition in these systems is unknown, this paper proposes that the polymer interacts with the surface of highly metastable subcritical sodium acetate clusters to prevent or prevent further growth into crystallites by a blocking mechanism, and in due course by This precipitated material. Figure 2 provides a proposed illustration of this mechanism.

Applicants have found that even when the polymer systems herein are seeded with SA to effectively force solid mass to form, the solid mass so formed is identical in appearance and performance to that observed for the corresponding solid mass formed in the non-polymeric system s difference. This has an impact on the properties of the resulting solid, indicating that different structural habits can exist in the solid, and the polymer acts as a habit modifier.

Whilst these modified polymers containing aqueous sodium acetate are indeed more unexpectedly and ideally resistant to SA formation, they are not suitable for application as PCMs because as the experiments and results discussed in this paper and the SA phase diagram in Fig. 1 clearly show, trihydrate Sodium acetate does not readily nucleate, even in supersaturated solutions, which means that a nucleating agent is required to promote nucleation of sodium acetate trihydrate in aqueous solution.

Nucleating agents as defined herein are also referred to as nucleating agents or nucleating accelerators. In some cases, the effective pairing of a particular nucleating agent with a particular material may be the result of the isostructural similarity of the nucleating agent and the hydrated salt in their crystalline forms, and indeed this is the case for many known pairings. For example strontium chloride hexahydrate as nucleating agent for calcium chloride hexahydrate, and sodium tetraborate decahydrate as nucleating agent for sodium sulfate decahydrate, in each pair they have very similar molecular arrangement.

Identifying sodium acetate trihydrate as a suitable nucleating agent was more challenging. While disodium hydrogen phosphate (DSP) and tetrasodium pyrophosphate (TSPP) have been identified as potential nucleating agents of SAT, their mechanisms of action are still unknown. (TWada和RYamamoto“Studiesonsalthydratesforlatentheatstorage.1.Crystalnucleationofsodiumacetatetrihydratecatalyzedbytetrasodiumpyrophosphatedecahydrate”,BulletinoftheChemicalSocietyofJapan.第55卷，第3603页，1982；TWada,RYamamoto和YMatsuo“Heatstoragecapacityofsodiumacetatetrihydrateduringthermalcycling”,SolarEnergy.第33卷，第373页至375页，1984；以及HKimura , "Nucleating agents for sodium acetate trihydrate", Journal of the Japanese Association of Crystal Growth. Vol. 9, No. 3, p. 73, 1982.)

Furthermore, these nucleating agents have a well-known so-called deactivation at high temperatures, which destroys their potential to pair with SAT-containing PCMs that are considered to be used in phase change systems, since by their nature PCMs are intended for long-term use, Reliable activity on demand is therefore required throughout the intended heating/cooling/reheating cycles.

Unexpectedly, applicants identified a particular hydrate, dihydrate of disodium phosphate, as the active nucleating species of SAT, and also showed that the application of this hydrate in aqueous polymeric solutions containing SAT as described in detail below will provide compositions well suited for use as PCMs in phase change systems. Compositions according to the present invention generally contain one or more nucleation promoters, each at a level independently from about 0.1% to about 5%, from about 0.2% to about 3%, from about 0.5% to about 2%.

Therefore the present invention provides in addition the composition containing sodium acetate trihydrate as phase change material, and it comprises:

(a) about 48% to about 60% anhydrous sodium acetate;

(b) from about 0.1% to about 10% of at least one suitable alkali-soluble polymer;

(c) from about 0.1% to about 5% of at least one suitable nucleation promoter; and

(d) The balance of water.

Alternatively, when sodium acetate trihydrate is used, the above composition becomes:

(a) about 80% to about 100% sodium acetate trihydrate;

(b) from about 0.1% to about 10% of at least one suitable alkali-soluble polymer;

(c) from about 0.1% to about 5% of at least one suitable nucleation promoter; and

(d) The balance of water.

Whilst any substance capable of nucleating a SAT is suitable for use herein, preferred substances that not only nucleate a SAT but also keep it effective at high temperatures are especially suitable for use in compositions used as PCMs according to the present invention. Such substances include: disodium hydrogen phosphate (DSP), tetrasodium pyrophosphate (TSPP), and hydrated forms thereof. Particular materials suitable for use herein are disodium hydrogen phosphate dihydrate and tetrasodium pyrophosphate decahydrate. Accordingly, the present invention provides a composition as defined hereinbefore, wherein the nucleation promoter is disodium hydrogen phosphate (DSP), tetrasodium pyrophosphate (TSPP), and hydrated forms thereof, at levels of each independently from about 0.1% to About 5%, about 0.2% to about 3%, about 0.5% to about 2%. Furthermore, there is provided a composition as defined hereinbefore, wherein the nucleation accelerators are disodium hydrogen phosphate dihydrate and tetrasodium pyrophosphate decahydrate, wherein the total level of these accelerators is from about 0.5% to about 5%, about 0.2% to about 2.5%, about 0.5% to about 2%.

Besides the polymer and the nucleation promoter, when used as PCM, the composition according to the invention may additionally comprise another agent which changes the melting point of SAT. Any suitable reagent which provides the desired melting point shift may be used, and for the avoidance of doubt, melting point shifting means lowering the melting and crystallization points. Such modifiers may be used at relative concentration levels of about 1% to about 25%, 5% to about 25%, about 10% to about 20%, about 2% to about 10% of the total mass. Examples of agents useful herein to lower the melting point of SAT in the compositions include: metal salts, such as lithium acetate dihydrate; and organic compounds, such as acetamide and trimethylolethane, which may also include non-metallic salts, such as ammonium acetate .

Therefore the present invention additionally provides as phase change material containing sodium acetate trihydrate composition, it comprises:

(a) about 35% to about 60% anhydrous sodium acetate;

(b) from about 0.1% to about 10% of at least one suitable alkali-soluble polymer;

(c) from about 0.1% to about 5% of at least one suitable nucleation promoter;

(d) from about 1% to about 95% of an optional melting point depressant; and

(e) The balance of water.

Preferred compositions herein wherein the level of lithium acetate dihydrate used as melting point depressant is from 1% to about 25%, from about 5% to about 25%, from about 10% to about 20%.

Lithium acetate dihydrate is 64.67% LiOAc and 35.33% water, the values below are copied from the values above but multiplied by 64,67.

Preferred compositions herein wherein the level of anhydrous lithium acetate used as a melting point depressant is from 0.65% to about 16.17%, from about 3.23% to about 16.17%, from about 6.47% to about 12.93%.

The melting point can also be lowered by adding acetamide and trimethylolethane.

The SAT-containing compositions of the present invention as PCM can be prepared according to the following process, which comprises:

(a) mixing an aqueous solution containing anhydrous sodium acetate with at least one suitable alkali-soluble polymer, at least one nucleation promoter, and at least one melting point depressant;

(b) heating the resulting mixture to provide a phase change material comprising sodium acetate trihydrate at 58°C.

According to the preferred method herein, about 35% to about 60% of anhydrous sodium acetate, a total amount of about 0.1% to about 10% of a suitable alkali-soluble polymer, a total amount of about 0.1% to about 5% is used in the mixing stage. % of one or more nucleation promoters, and optionally include from about 1% to about 25% of a melting point depressant. An example of this method can be found in Example 3 below.

According to the preferred method herein, about 35% to about 60% of anhydrous sodium acetate, a total amount of about 0.1% to about 10% of a suitable alkali-soluble polymer, a total amount of about 0.1% to about 5% is used in the mixing stage. % of one or more nucleation promoters, and optionally include from about 1% to about 95% of a melting point depressant.

Alternatively, the polymer can be formed in situ in the molten (heated) aqueous SAT mixture, in which case the relevant monomers will be added to the aqueous solution and polymerization will begin. Thus, the PCM can be prepared in the thermal battery enclosure prior to incorporation into the heat exchanger and sealed, or the PCM can be prepared in an external container and then poured into the enclosure containing the heat exchanger.

The following non-limiting examples, provided by the experimental results below, are typical of PCM compositions and methods for their preparation according to the invention.

Experimental results

Example 1: Addition of Polymer 1 to aqueous sodium acetate to prevent precipitation

1% (2 g) of poly(methacrylic acid-methyl methacrylate) 2:1 copolymer has a molecular weight of about 500,000-1,000,000 (available from Fluka as polyacrylic acid, CAS Reg. No. 25086-15-1, marked as Medium viscosity, number average molecular weight 500,000-1,000,000, copolymer of methacrylic acid and methyl methacrylate), at a concentration of 58.24% (17.002 mol·dm ^-3 ) of the copolymer at about 60°C to about 70°C Add to a well mixed 198 g of aqueous sodium acetate solution (99% anhydrous sodium acetate from VWR International Limited (UK)) with stirring, then cool to room temperature (RT).

At room temperature, a homogeneous liquid was observed, which was in sharp contrast to the same solution without any polymer, where a clear precipitation of sodium acetate was observed. In addition, cycling experiments were performed throughout the temperature range of about 25 to about 80°C, which demonstrated that the beneficial effects observed for the polymer-assisted solutions were consistent across the range tested. Furthermore, further experiments confirmed the formation of sodium acetate seeds only at room temperature.

Example 2: Addition of polymer 2 to aqueous sodium acetate to prevent precipitation

According to the method of Example 1, (0.66% for polymer only) 22.6 g of poly(methacrylic acid, sodium salt) with a molecular weight of 9,500 (poly(methacrylic acid, sodium salt) , the average number average molecular weight of the solution measured by gel permeation chromatography is 5,400, the average weight average molecular weight is 9,500, the weight percentage in water is 30wt.%, and the CAS registration number is 54193-36-1) 30% aqueous solution is added into 59.16% (17.66 mol·dm ^-3 ) sodium acetate aqueous solution (1,000 g), and then cooled to room temperature (RT).

Example 3: Verification that the polymer system has a homogeneous liquid at 58°C

Test samples containing various levels of polymers 1 and 2, and different initial liquid concentrations of sodium acetate were left to stand at room temperature for several weeks. Sodium acetate was observed as a large white mass occupying the entire sample container. This mass was thought to be a complex mixture of sodium acetate and water, but had the appearance of a solid. When the sample container was squeezed, the mass was observed to be very soft. Carefully agitate the agglomerate, and fine needle-like crystals can also be found. Further, the sample was heated to 58°C to obtain a homogeneous liquid, which is consistent with point 2 in the phase diagram in Figure 1, as described above.

In addition, the test sample was carefully seeded with sodium acetate, also left standing, the resulting sodium acetate appeared as a large white mass occupying the entire sample container. This mass was thought to be a complex mixture of sodium acetate and water, but had the appearance of a solid. When the sample container was squeezed, the mass was observed to be very soft. Carefully stir the agglomerate, and fine needle-like crystals can also be found. Further, these samples are homogeneous liquids when heated to 58°C, which is consistent with point 2 of the phase diagram in Figure 1.

The ability to form a homogeneous liquid without the need to add excess water is in stark contrast to that observed for precipitation systems without polymer. However, the observed improvement in both homogeneity and thermodynamic stability of the system of the present invention with polymer compared to sodium acetate trihydrate without polymer, after cooling and reheating, is truly revolutionary.

Example 4: Identification of the active nucleating agent DSP of SAT

Application of varying temperature powder X-ray diffraction to identify dibasic sodium phosphate dihydrate as an active nucleating agent. Cooling a sample of sodium acetate trihydrate with disodium hydrogen phosphate dihydrate crystallized sodium acetate trihydrate. The sample was heated to 90°C to convert the dihydrate to anhydrous disodium hydrogen phosphate. This sample, now containing SAT and anhydrous DSP, was then cooled to 25°C, and the anhydrous DSP did not change back to dihydrate DSP, so crystallization of sodium acetate trihydrate could not occur.

Additional experiments were performed to confirm that no deactivation of the system occurred, either by seeding with sodium acetate trihydrate or with active nucleating agents, at the temperatures required for use in compositions as PCM. The results of these experiments confirmed that upon this seeding, the nucleating agents were "activated" and their potency was fully restored. This is consistent with previous observations, but applicants are the first to understand and characterize this hitherto unexplained phenomenon.

Embodiment 5: the preparation of the PCM formula containing SAT

PCM1 PCM2 Material % by weight % by weight polymer 0.67% 0.67% sodium acetate 56.2% 44.45% water 40.31% 31.87% DSP 2H ₂ O 1.20% 1.29% TSPP·10H ₂ O 1.62% 1.73% LiOAc·2H ₂ O - 20%

Formulation 1 was prepared as follows: anhydrous sodium acetate (134.1 kg, 1634.77 mol), water (94.6 kg, 5251.18 mol) and polymethacrylic acid polymer (molecular weight 9,500) as a 30% aqueous solution (5.3 kg), DSP (2.3 kg, 16.20mol) and TSPP (2.3kg, 8.65mol) were mixed together and then heated to about 70°C. The resulting 58°C PCM prepared by this method does not form anhydrous sodium acetate.

Recipe 2 was prepared as Recipe 1. The prepared PCM at 50°C also does not form anhydrous sodium acetate.

Thus, the PCM according to the invention does not contain SA when observed with the naked eye as well as experimental techniques such as x-ray powder diffraction.

Example 6: Addition of Acetamide to Sodium Acetate Trihydrate to Lower Melting Point

Ratio of SAT to acetamide in the mixture

a) Starting from the trihydrate form of sodium acetate:

Made to contain 95.53wt% sodium acetate trihydrate (CAS6131-90-4), 2.17wt% water and 2.30wt% poly(methacrylic acid, sodium salt) (purchased from SigmaAldrichUKCAS registration number is 54193-36-1 ) in water, which is heated to 60-70°C while stirring to form a homogeneous mixture.

b) Starting with anhydrous sodium acetate:

57.85wt% sodium acetate (available from VWR International Co., Ltd., 99% anhydrous sodium acetate, CAS127-09-3), 39.84wt% water and 2.31wt% poly(methacrylic acid, sodium salt) aqueous solution heating to 60-70°C while stirring to form a homogeneous mixture.

To lower the melting point and freezing temperature, various amounts of acetamide were added to the solution as indicated in the table above. The melting temperature and freezing temperature (with seed crystal nucleation) of the samples were recorded and the range of reduction is shown below. Crystallization temperatures of 58°C to 28.5°C can be obtained by adding acetamide in mole fractions up to 70%, and the mixture then approaches the eutectic point, after which point the freezing temperature increases. This is shown in FIG. 3 .

Example 7: Adding Trimethylolethane to Sodium Acetate Trihydrate to Lower the Melting Point

A solution of sodium acetate trihydrate was prepared as described in Example 1. Mixture samples were prepared by adding SAT solution to TME as described in the table below.

This mixture can be manually nucleated with seed crystals, or 2 wt % disodium hydrogen phosphate dihydrate nucleating agent. By increasing the mole percent of trimethylolethane from 0 to 40%, the material has a freezing point of 42°C to 58°C.

Claims (15)

1. A composition containing sodium acetate trihydrate as a phase change material, comprising: (a) sodium acetate trihydrate or sodium acetate anhydrous; (b) one or more suitable alkali soluble polymers; (c) one or more suitable nucleation promoters; and (d) water. 2. Composition according to claim 1, characterized in that the level of sodium acetate trihydrate is from about 80% to about 100% by mass of the composition. 3. The composition according to claim 1, characterized in that said anhydrous sodium acetate is present at a level of from about 45% to about 60% by mass of said composition. 4. Composition according to claim 1 or 3, characterized in that the level of said one or more alkali soluble polymers is independently from about 0.1% to about 10% by mass of said composition. 5. Composition according to any one of claims 1 to 4, characterized in that the one or more alkali soluble polymers are polymers of general formula I. 6. A composition according to any preceding claim, wherein the one or more alkali soluble polymers are independently selected from copolymers of methacrylic acid and methyl methacrylate, having a molecular weight of from about 500,000 to about 1,000,000 poly(methacrylic acid-methyl methacrylate), or a sodium, potassium, or zinc salt thereof; poly(methacrylic acid) having an average molecular weight of about 10,000, or a sodium salt thereof; or mixtures thereof. 7. A composition according to any preceding claim, wherein the level of one or more suitable nucleation promoters is independently from about 0.1% to about 5% by mass of the composition. 8. Composition according to any preceding claim, characterized in that said one or more suitable nucleation promoters are independently selected from: disodium hydrogen phosphate (DSP) and hydrates thereof, tetrasodium pyrophosphate (TSPP) and hydrates thereof, and mixtures thereof. 9. Composition according to any preceding claim, characterized in that the nucleation promoters are disodium hydrogen phosphate dihydrate and tetrasodium pyrophosphate decahydrate at a total level of about 0.5% by mass of the composition % to about 5%. 10. A composition according to any preceding claim, further comprising an agent for altering the melting point of sodium acetate trihydrate at a level of from about 1% to about 95% by mass of the composition. 11. Composition according to claim 10, characterized in that said agent is lithium acetate dihydrate. 12. Composition according to claim 10, characterized in that said agent is anhydrous lithium acetate. 13. A process for preparing a composition containing sodium acetate trihydrate as a phase change material according to any preceding claim, comprising: (a) mixing an aqueous solution comprising anhydrous sodium acetate, at least one suitable alkali-soluble polymer, and at least one nucleation promoter; (b) heating the resulting mixture to provide a phase change material comprising sodium acetate trihydrate at 58°C; and Wherein said aqueous solution may optionally contain a reagent for changing the melting point of sodium acetate. 14. The method according to claim 3, wherein said aqueous solution comprises: about 40% to about 60% of anhydrous sodium acetate, about 0.1% to about 10% of at least one suitable alkali-soluble polymer, about 0.1% to about 5% of at least one suitable nucleation promoter, about 1% to about 25% of an optional melting point depressant, and the balance water. 15. Use of a composition according to any one of claims 1 to 10, or a composition obtainable by a process according to claim 11 or 12, as a phase change material.